.TH cachetop 8  "2016-01-30" "USER COMMANDS"
.SH NAME
cachetop \- Statistics for linux page cache hit/miss ratios per processes. Uses Linux eBPF/bcc.
.SH SYNOPSIS
.B cachetop
[interval]
.SH DESCRIPTION
This traces four kernel functions and prints per-processes summaries every
\fBinterval\fR seconds. This can be useful for processes workload characterization,
and looking for patterns in operation usage over time. It provides a \fBtop\fR-like interface
which by default sorts by \fBHITS\fR in ascending order.

This works by tracing kernel page cache functions using dynamic tracing, and will
need updating to match any changes to these functions. Edit the script to
customize which functions are traced.

Since this uses BPF, only the root user can use this tool.
.SH KEYBINDINGS
The following keybindings can be used to control the output of \fBcachetop\fR.
.TP
.B <
Use the previous column for sorting.
.TP
.B >
Use the next column for sorting.
.TP
.B r
Toggle sorting order (default ascending).
.TP
.B q
Quit cachetop.
.SH REQUIREMENTS
CONFIG_BPF and bcc.
.SH EXAMPLES
.TP
Update summaries every five second:
#
.B cachetop
.TP
Print summaries each second:
#
.B cachetop 1
.SH FIELDS
.TP
PID
Process ID of the process causing the cache activity.
.TP
UID
User ID of the process causing the cache activity.
.TP
HITS
Number of page cache hits.
.TP
MISSES
Number of page cache misses.
.TP
DIRTIES
Number of dirty pages added to the page cache.
.TP
READ_HIT%
Read hit percent of page cache usage.
.TP
WRITE_HIT%
Write hit percent of page cache usage.
.TP
BUFFERS_MB
Buffers size taken from /proc/meminfo.
.TP
CACHED_MB
Cached amount of data in current page cache taken from /proc/meminfo.
.SH OVERHEAD
This traces various kernel page cache functions and maintains in-kernel counts, which
are asynchronously copied to user-space. While the rate of operations can
be very high (>1G/sec) we can have up to 34% overhead, this is still a relatively efficient way to trace
these events, and so the overhead is expected to be small for normal workloads.
Measure in a test environment.
.SH SOURCE
This is from bcc.
.IP
https://github.com/iovisor/bcc
.PP
Also look in the bcc distribution for a companion _examples.txt file containing
example usage, output, and commentary for this tool.
.SH OS
Linux
.SH STABILITY
Unstable - in development.
.SH AUTHOR
Emmanuel Bretelle
.SH SEE ALSO
cachestat (8)
